A common assisted reproduction technology, in-vitro fertilisation (IVF) and its derivatives, allows for the retrieval of male sperm & female oocytes by various methods. This is followed by immediate use or storage of these gametes. Fertilisation of the oocyte(s) under strictly controlled conditions occurs immediately or at a later date. Embryos formed by this process are grown in optimal surroundings for a variable time in the laboratory and assessed. The embryos are then replaced in the genital tract, most commonly the uterus, of the female where they will hopefully implant in the endometrium of the uterus, leading to an ongoing pregnancy.
There are many potential points of failure in this overall process. Success rates of IVF have increased slowly but gradually over time. An important step in the IVF process is the replacement of the embryo in the female, most commonly in the uterus. In this step, the clinician examines the female and exposes the uterine cervix with a speculum. The cervix is cleaned. A catheter is inserted through the cervix into the uterine cavity. International Patent Application No PCT/US00/26313 (Cook Urological Inc) describes a prior art embryo transfer catheter designed for this purpose. Ultrasound is often used to guide placement. This catheter may be stiff to enable more forceful passage through the cervix, which can be tortuous. Alternatively, the catheter can be soft to allow a passage that follows the anatomy without forcing. Some catheters have both hard and soft sections.
A further internal catheter is inserted through this outer catheter, and its distal end protrudes from the outer catheter as the outer catheter is possibly withdrawn slightly. The inner catheter is then positioned, optimally under ultrasound control, to a point near the fundus, or top, of the uterine cavity. Better results are obtained if this inner catheter is soft and passage is atraumatic. Finally, when correct placement has been judged, a further cannula containing embryos, culture fluid for nourishment, and sometimes air bubbles to aid ultrasound visualisation, is rapidly deployed through the inner catheter, flushed to eject the contents, and then withdrawn with checks to confirm the embryos have been ejected into the uterus. When this is confirmed, all catheters are withdrawn and the patient rests for a variable amount of time. An older technique uses only two catheters, and the inner catheter is used for both positioning and transfer of embryos.
There are several ways that success rates may vary that are attributable to this embryo transfer step in the assisted reproduction process:                1. Passage of the outer catheter though the cervix might be difficult. Manipulation or forceful passage of the catheter leads to irregular contractions in the uterus. When the embryos are inserted, these contractions can lead to the embryos ending in the Fallopian tubes where they may become ectopic pregnancies. Alternatively, contractions may lead to the embryos flushing out through the cervix once the transfer catheter is removed. There is research to show that the number and quality of irregular contractions is correlated with success or failure of embryo transfer. Also, there is research showing reduced success if there is blood and mucus, a sign of traumatic insertion, on the catheter once withdrawn.        2. There may be sub-clinical infection present at the cervix. There is research showing reduced pregnancy success when there is mucopurulent discharge visible at embryo transfer.        3. Following removal of the embryo transfer cannula, the embryos may be expelled from the uterus prior to their implantation. This may be the case even if transfer is easy. Varying periods of bed rest to reduce this chance have been tried with inconclusive results.        4. Even if the embryos remain in the uterus, there may be uterine conditions that prevent or reduce implantation. One reason is the total area of healthy endometrium available for implantation may be reduced by fibroids or a septum in the uterus. Another reason might be that the endometrium has not responded well to hormonal manipulation prior to transfer, and is less receptive. There may be subclinical infection in the cavity or endometrium, perhaps exacerbated by passage of the catheter through an infectious cervix.        
Therefore, it could be postulated, embryo quality and other maternal factors being equal, that:Implantation rate∝Area and quality of endometrium*Time in the cavity to allow implantation
The present invention was developed with a view to providing a new embryo transfer catheter which may be left securely in situ before and after embryo transfer for several days or longer and which minimises physical disturbance of the endometrium at the time of embryo transfer, and inhibits expulsion of embryos. The invention also provides an improved method of transferring an embryo into the uterine cavity. Although the embryo transfer catheter and method will be described with particular reference to human use, it will be understood that the device and method may also be used with animals.
References to prior art in this specification are provided for illustrative purposes only and are not to be taken as an admission that such prior art is part of the common general knowledge in Australia or elsewhere.